When Two Are Not Enough
by MrsCumberbatch
Summary: John Watson is bi. Sherlock Holmes still has to find out what he likes. Mary Morstan wants a threesome. Mrs Hudson is out of town. And in 221 B Baker Street people want to have fun.
1. An Idea

**I don't know where this came from, but feedback will be highly appreciated. **

* * *

**Chapter one: An Idea.**

John took a deep breath when he felt _him_ joining them. The doctor was pretty sure everything was a mistake and yet he didn't want him to go. Mary said that sometimes _two weren't_ _enough_.

The idea of a threesome wasn't entirely bad.

To begin with, it was a fantasy both shared.

It was the kind of fantasy John had never been part of. Actually, it was one of those things John wanted to experience before dying. Well, being in a threesome was something to be remembered and laugh at when old.

Mary was straight.

John was bi.

There you have the reason why they knew they needed a third part involved.

And that third part ought to be a man.

Something Mary said turned her on was thinking of John Watson with a man. 'Three continents' Watson was a story that eventually Mary heard of and the idea of a threesome came when she said she wanted to experiment.

John agreed. Mary was happy.

They discussed several scenarios: Mary watching John and another man having sex, Mary and John having sex and the third man watching; Mary and the other man having sex and John watching.

Or the three of them having sex.

Mary laughed and said they shouldn't think of it, that they should actually let that happen without thinking about it.

Mary said premeditating things would make the entire experience stupid.

John agreed.

However, when Mary said she would find the perfect man, John never imagined who she had already in mind.

Never, but never ever was John Watson imagining Sherlock _asexual_ Holmes joining him and Mary in bed.

Never.

But yet, there he was. There was the _asexual_ Sherlock Holmes kissing Mary, practically devouring her with his stupidly soft lips.

There was Mary Morstan, the lovely woman everyone said looked like an angel, stroking Sherlock's hard member while being devoured by Sherlock Holmes.

And there was he, John Watson, the man no-one ever dared to call a bad lover watching Mary being devoured by Sherlock Holmes. And at the same time, there was he, John Watson, being sexually aroused by Sherlock Holmes and his calloused yet ridiculously long fingers wrapped around his prick.

And there were they, limbs tangled, the three of them completely naked, a box of condoms sitting next to the bed as well as a bottle of lube, a pair of handcuffs and a riding crop.

And there was the _asexual_ Sherlock Holmes commanding the whole thing, telling Mary where to touch John, where to touch him and handcuffing the good doctor to the bed.

John Watson closed his eyes and wondered why he never said no to Mary when she said she wanted Sherlock to join them. And why he said no when she said she wanted to watch.

After all, Mrs Hudson was out of town.

And in 221 B Baker Street people want to have fun.

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**Next chapter: The proposal. **


	2. The Proposal

**Chapter two: The proposal**

Sherlock Holmes had to admit Mary Morstan was a clever woman.

Clever enough to show up at his flat, at tea time when the kettle had just boiled wearing a tight short skirt, a too revealing, almost transparent shirt, high heels and dark stockings. Actually, clever enough to reveal, by the way she looked, what she was looking for.

Clever. Brilliant.

Brilliant impression of an idiot.

But still... sexy.

"John doesn't know you're here."

She smiled. "No."

You don't need to be Sherlock _bloody_ Holmes to know what that woman was looking for.

"No."

"Is that your answer?"

"Yes."

"You don't even know what I'm going to ask you."

Sherlock raised an eyebrow and said softly, "I don't need to know. I can _see_ it." He poured tea into his cup and reached for the milk. "Milk?"

"Oh, yes," she licked her lips. "Please, _Sherlock._"

The detective handed her the tea cup and their fingers brushed just slightly.

Slightly enough for Sherlock to feel Mary's warm skin. Warm. Almost burning. Heat. Not temperature. Heat... the state de sexual excitement.

"He will say no."

"Is that what you think?"

"I don't think. I_ know_."

Mary smiled but this time she crossed her legs, seductively, and licked her red painted lips like an animal about to devour her next victim. "I've observed you, Sherlock."

Oh really? "Have you?"

"Oh yes," Mary almost panted. "We're both adults so lets talk about this clearly, shall we? I've seen the way he looks at you," she almost sang. "And the way you look at him. John is bi. You're friends but I bet he fantasized about you."

Sherlock was aware of Miss Morstan's procedures. He knew how she enchanted John. He knew what they did within the four walls of their room in their new flat and what they used to do within the four walls of John's room when the good doctor still lived with him. It was not so difficult to see both were very sexual. After all, that's how their relationship started. John Watson was a very sexual man, something Sherlock often remarked only to push the doctor's buttons. Sherlock could tell when a woman was only interested in John's dick, and when he often made the good doctor know so, John would say _'bollocks'_. But if one night John had a slightly little problem and after a bad sexual performance and the lady didn't answers his calls the following day, Sherlock Holmes would say _'I told you so'. _

It was true. Sherlock often found John looking at him in a way you don't look at your flatmate and friend.

And Sherlock often found himself looking at John in a way you don't look at your blogger and best friend.

"And you," Mary said before Sherlock could have said something. "You still don't know what you like, dear. I've seen the way you look at me. John told me about Irene Adler. And you're _not_ a virgin."

And Sherlock often found himself looking at Mary in a way you don't look at your friend's partner.

Now he was surprised. If he ever thought of Mary Morstan as mundane and common as any other woman he met he was so, _so_ wrong. Indeed he was. He _was_. Mary Morstan was neither mundane nor common. Mary Morstan knew what she wanted and how she wanted it.

But she was John's girlfriend.

And she was right. Right about everything. Damn, he was not a virgin and she was the only one who knew it. Everyone thought he was a virgin, asexual, yes. But not a virgin any more. Both genders had bored him.

This was a good challenge.

The detective felt blood rushing south. "Tell me, miss Morstan, how have I looked at you?"

"Like you're looking at me _now._" Mary leaned forward, thrusting her breasts up for the detective to look at. "You heard us once, remember? It turned me on, you know, knowing that you were here, experimenting and I was up there with John, having the most mind blowing sex ever."

Now he was having an erection. "What if he says no?"

"He won't. He's looking forward to this as much as we are, Sherlock dear."

Something in her blue eyes made the detective weak. She walked until she was standing next to him and took his hand. She guided it to her breasts and he squeezed, not softly yet not roughly. "Mary..."

"It feels good, doesn't it?" Mary whispered, brushing their lips just slightly. "We're friends, Sherlock. This could be our little secret. No one needs to know."

He assented.

He actually _assented._

"John will want to set rules."

She smiled. "_Of course._ Think of yours. I have already set up mine."

"When?"

"Next Friday. Mrs Hudson is out of town so I think we could always use John's old room, don't you think?" Mary winked at him. "Get ready, Sherlock love. We'll bring the condoms, you don't forget the lube."

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**Next chapter: Setting the rules  
**


	3. Setting the Rules

**Chapter 3: Setting the rules**

"Is not that I don't mind -" John said between mouthfuls of Chinese. "I... I know this is what you want."

What a way of putting it. "We don't need to do it if you don't want to, John."

"Mary."

"I _mean_ it!" Mary smiled. "It's very... I don't know," she chewed her lip. "We agreed we'll only be doing this if we were both OK with it."

"I'm OK with this."

She frowned. "You sure?"

"Yes. Have you been into any website?"

"I've found him."

"Oh. What's he like?"

"You'll like him."

"We need to set up rules."

"I'm all ears," Mary said, drinking her wine.

"If anyone says 'stop', we stop." John said. "Condoms all the time," Mary nodded to that. "Um, that's practically all."

Mary nodded. "When I suggested this, I did it because I knew it was something we both wanted to try," John smiled at her reassuringly. "We're solid and that's very important... because this could be the best we thing we could do."

"I know."

"Or this could end our relationship."

Now John wasn't expecting that. "What?"

"Exactly, John," Mary said, her face serious this time. "You said you wanted me to enjoy this. I want you to enjoy this _too._ And I don't want you to think wrong of me, or neglected."

"I won't."

"You're saying this now."

"I won't," John repeated. "This will be all about you. That's how I want it."

"John, if you want to cancel this, tell me."

"I don't."

"You sure?"

John kissed Mary. "Of course."

"I want to watch too."

Now John didn't know what to say.

**Meanwhile, in 221 B Baker Street...**

Rules. She said he had to think about rules. Rules... what rules he could think of? The ones setting up the rules were and _should_ be them, not him. After all, Sherlock was sure John was not going to let this happen.

Of course John was walking out of this as soon as he realised it was him joining them in sex.

John was so vanilla.

John would never let him have sex with Mary. Because, after all, that was all about. Mary said it was her and them. She said John wanted to watch. But she wanted to watch too.

Now, the thing was: what to do? What to think of? Mary said it was male-female-male, according to John's wishes. But according to hers, she wanted it to be male-female-male, female-male-male and male-male. She said she wanted to watch.

Mary said she wanted him and John to do it.

And she would watch.

It wasn't as twisted as Sherlock had predicted it could be.

How to proceed?

What will she be like?

Mary Morstan was not a difficult person to deduce. She was right, he had heard them once and for what he heard, it was rough, almost violent. Not difficult. Mary Morstan, surely soon Mary Watson, was not a woman who would want gentleness but directness. After all, she was a woman acclimatised to violence since she had been through a nasty marriage and a very much awful divorce.

Now John. Mary was right again, damn woman, John was obviously joining the game. Will John want to have sex with him? Had John fantasized with him?

Sherlock didn't know what to expect.

But he already had lube, a pair of handcuffs and a riding crop sitting on his beside table.

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**Next chapter: Dinner and foreplay**


	4. Dinner and foreplay

**Chapter 3: Dinner and foreplay**

The man was coming for dinner. Mary said it would be fun to talk a bit and discuss the rules before the action. But at the last moment, Mary said they were going to the man's place.

She asked the cabbie to drive to Baker Street.

"Baker Street? It wouldn't be near Sherlock's, would it?"

Mary smiled. "Don't be silly, John."

"The last thing I need is Sherlock knowing we shagged the guy across his street."

The cab stopped at 221 Baker Street and in mere seconds Mary was ringing Sherlock's bell.

No way. No. No. No. Just... no.

"Hello Mary, John."

Why were they at Baker Street? Why were they drinking wine? Why was Sherlock wearing new clothes and a tight shirt? Why was Mary wearing no underwear under her dress? Why was there a big box of condoms sitting on the table?

And why the fuck he never saw this coming?

"You don't look so happy, dear."

"Why Sherlock?"

Mary looked at him as if what he had just asked was obvious. "You wanted me to find the perfect -"

"You could've chosen any other man from any of those swinging sites we looked at!" John bellowed. "Not... him!"

Sherlock looked at him, slightly hurt. "Why not?"

"Why not?" John repeated.

"Yeah, why not?" Asked Mary, confusedly. "He's a friend -"

"Exactly!

Mary laughed. "John, please, don't be so boring. Sherlock is our dear best friend. He's our only and _best_ option. Nothing like little secrets between friends, right?"

No fucking way.

And then, just then, she was sitting next to him and Sherlock had a hand on her bare thigh.

And he was squeezing. Sherlock was moving his hand slowly on her bare thigh, experimenting, exploring, caressing her soft skin. That soft skin John had always enjoyed so much. His long fingers were wrapped on her leg and without even looking at her John could tell Mary was going wet. It was written in her face, in the way she looked at him, in her now pink cheeks, in the way she sat very close to Sherlock until he, with a quick movement, made her sit on his lap, glueing her back to his chest, opening her legs for John to watch and then he moved a hand further into her, to her womanhood.

"You said you wanted to watch," John almost growled.

But before Mary could speak, Sherlock moved his hand forward and Mary made a choking noise. "Oh God."

"This is more fun. If any other man was here, doing what I'm doing right now, you wouldn't have complained. But as it is me and not any other man, you're jealous."

"Of course -"

"But not like that," Sherlock spoke softly, sending Mary shivers down her spine. "You feel neglected. Don't be so obtuse John. I'll get my hands on you soon."

No. fucking. way.

"Have you already set up your rules, darling?" Mary purred, still sitting on Sherlock's lap, her legs still wide apart for the detective's hand to explore her, for John to watch when she started moving the front zip of her dress down. "Because here John and I have some."

"This is us here," Sherlock said, his eyes on John. He licked the skin of Mary's neck and continued working on her clitoris. "No acting. I can do you both, but of course, if John here agrees."

"Of course he... oh God, Sherlock, your hands. Stop it or I'll come."

Sherlock chuckled darkly. "That's the idea."

John stood up. "I'm out of this."

Sherlock immediately stopped touching Mary and she stood up too. "What?"

"I'm not seeing you having sex with... him!" John said angrily. "And I'm not-" he looked at them as if they were mad and as if he were the only person sane. "I'm not having sex with _him_!"

"John, please," Sherlock said from his place. "You're bisexual. You like cocks more than vaginas. You've fantasised with me. You have wondered what could be like to have me, to posses me. Don't lie to me. It's all written on your face."

That was awfully true.

True, true, true.

Damn. "I'm out of this."

"Are you?" Sherlock insisted. "Because I know before you moved out you and Mary had sex upstairs and it turned you on, knowing I was here, that I could listen to you both."

"John, he's a friend. Everything will be OK, I promise."

Something in Mary's voice made him reconsider the whole thing.

"Got lube?"

Sherlock made a gesture with his head. "My room."

This was going to be fun.


	5. Let's Get it Started

**Author's note: For a more smutty version you can find this fic in AO3. **

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**Chapter 4: Let's Get it Started**

John knew this was a bad idea as soon as he watched Mary being pushed against a wall. Plus, she was being devoured by Sherlock Holmes and his stupidly soft lips and he was also undressing her.

He was undressing her.

_OK John Watson, breathe. Just breathe. Mary promised everything was going to be OK. Just in a few hours everything's going to end and you and Mary will go home and get some sleep and tomorrow morning we can pretend nothing happened. You'll still solve crimes with Sherlock and neither of us will remember we had sex with the same woman. In a month or two you'll ask Mary to marry you and we'll have one to two children and we'll never talk about this again._

John repeated all those sentences once, two, three and four times until Mary was on her back on the bed, her legs spread wide apart and the detective between them.

What the fuck!

And then, just like that, a cold hand was unzipping his trousers and freeing his cock and then-

"Oh, fuck -"

Sherlock's lips were wrapped around his prick while Mary was touching herself, and watching them.

John would never be able to tell how the two of them, Mary and Sherlock, managed to get him off all his clothes and suddenly the three of them were as naked as the day they were born.

"Look at you," Mary said seductively, standing between the two of them. "God, this is going to be a long night, right, Sherl, love?"

_Sherl, love?_ John didn't know what to say nor do when, standing behind Mary she moved her hips backwards as Sherlock moved his forwards, pushing her into John.

Mary was being pressed tightly against the two of them and she was enjoying it.

It had been implicitly agreed that it was all about the lady there.

And the lady wanted to fuck both.

At the same time.

Suddenly, both men were on their backs and Mary was kneeling between them, a hand wrapped in each of them, moving her slender fingers up and down their dicks and doing what she called 'getting them hard enough'.

Weren't they hard enough?

John looked at Sherlock and the man looked as if he was heaven and everything felt delicious, soft, good and sexy and no. John couldn't feel that way no matter how hard he tried. He couldn't help it. His girlfriend and soon to be wife (hopefully) was giving him the best handjob ever and surely she was going to give him a blowjob equally as perfect as this but no, this was not right.

Not at all when now Mary said she wanted Sherlock to fuck her pussy and John to fuck her from behind.

"I don't mean to be a bad girl, John," she purred as she climbed in between them and let a finger run on their chests. "But I always wondered what he could be like."

Sherlock chuckled. "I can say the same."

What?

"Don't be boring, John," Sherlock said and tore a foil open. "Let's get the lady ready."


End file.
